The sliding patio door has proved to be immensely popular in the past thirty years despite several obvious drawbacks. The standard patio door for example, cannot be locked from the outside, despite the fact that ingress and egress from such a door may be the most convenient access to the building. Further, such doors are extremely vulnerable to forced entry by burglars even when they are properly locked from the inside. Such doors may simply be lifted within their housing, pivotally swung outwardly and the entire door may be removed without forcing the lock.
Interior mounted door locks such as Sodenkamp, U.S. Pat. No. 3,709,539, Jan. 9, 1973 which are mounted on the floor prevent horizontal sliding of the movable panel, but they do not prevent entry if an illegal entry is performed by simply lifting the panel out of the frame as above described.
Robins, U.S. Pat. No. 3,886,771 provides secure exterior locking but the entire lock housing must be removed each time the door is unlocked. Imer, U.S. Pat. No. 3,863,470 provides exterior locking. The assembly is a lightweight "pop out" with an exposed lock cylinder barrel which can be easily twisted off with a common pipe wrench.
A more secure locked patio door is taught by Zelt, U.S. Pat. No 3,869,887 but the lock must be mounted inconveniently at the base of the door or in a hard to reach position at the very top of the door.